This invention relates to warewashers, such as dishwashing machines, and more particularly to a vented metering system for reliably and consistently dispensing a precisely determined quantity of liquid sanitizing agent independently of ambient conditions.
Warewashers having sanitizing systems for chemically sanitizing foodware items are known in the prior art. A particularly effective system, which utilizes air transport for reliably delivering a liquid sanitizing agent with a minimum of servicing and maintenance requirements is shown in U.S. Application Ser. No. 835,197, filed Sept. 21, 1977, Ser. No. 788,039, filed Apr. 15, 1977, Ser. No. 835, 198, filed Sept. 21, 1977, and Ser. No. 875,868, filed Feb. 7, 1978, all assigned to the assignee of the present application.
However, due to changes in external conditions, such as supply voltages, pressures, ambient atmospheric conditions, and so on, the above dispensers can be subject to fluctuations and variations in the amount of liquid sanitizing agent which is delivered. That is, since air is a compressible fluid, changes in barometric pressure, ambient temperature, humidity, altitude, the level of sanitizing agent in the supply bottle, compressor speed (due to voltage fluctuations), valve leakage in the air compressor, and so on, can all contribute to inconsistencies in the performance of air driven aspirators. In going from sea level to an altitude of approximately 10,000 ft., for example, the amount of liquid sanitizing agent delivered by the systems described in the above applications could be expected to be reduced by as much as 50%.
Of course, variations in the rate and the amount of sanitizing agent which is delivered have long been recognized as problems in chemical sanitizing machines, regardless of the mechanism by which the sanitizing agent is delivered. With water driven venturis, not only were deposits of minerals in the venturi a source of continuing trouble, but variations in line pressure and atmospheric conditions usually caused variations in the quantity of sanitizer which was delivered.
There is thus a need for a system which effectively and reliably delivers a predetermined quantity of liquid sanitizing agent each time the system is cycled. The system should be durable, easily maintained, uncomplicated, inexpensive, and suited for use in a wide variety of applications.